1. Technical Field
The present invention relates to a key switch sheet and a key switch module. Specifically, the present invention relates to a key switch module substrate used in a key switch used by being incorporated in a mobile telephone, or the like; a key switch module having a key top arranged on the key switch module substrate; and a key switch sheet for fixing a contact spring of the key switch module substrate.
2. Related Art
In mobile telephones and the like, a key switch having a structure in which a key is pushed with a finger thereby deforming a contact spring underneath, conducting electrode portions by the contact spring and turning ON the switch is used. In such a key switch, a raised dome-shaped contact spring is arranged on a second contact portion formed to surround a first contact portion, the first contact portion is covered by the contact spring while being spaced apart from the first contact portion, and the front surface side of the contact spring is covered with a contact spring fixing sheet. In the key switch, the contact spring deforms when the key is pushed with the finger thereby contacting the first contact portion, so that the first contact portion and the second contact portion are electrically conducted by way of the contact spring thereby turning ON the relevant switch. When the finger is released from the key, the contact spring elastically returns to be spaced apart from the first contact portion, and the switch returns to a OFF state.
In such a key switch, the click feeling of when the key is pushed with the finger becomes an important issue since the stroke of the key is short, and various methods for improving the click feeling have been proposed.
For instance, in a key switch module disclosed in FIG. 1 of Japanese Unexamined Patent Publication No. 2004-55389 (Patent Document 1), an apex portion of the contact spring is fixed to the back surface of a fixing sheet, and a resin material is stacked and solidified in one layer or a plurality of layers at the front surface of the fixing sheet at a position corresponding to the apex portion of the contact spring to thereby form a resin dimple (projecting portion) at the front surface of the fixing sheet (see claim 3 of Patent Document 1). A satisfactory click feeling is obtained by pushing such a resin dimple with a pushing portion (pusher) arranged on the key, and deforming the contact spring with the resin dimple.
However, in the structure of Patent Document 1, the resin dimple is formed by adding the resin material to the front surface of the fixing sheet fixed with the contact spring, and thus processing of the fixing sheet is difficult. The cost of the fixing sheet greatly rises even if the resin dimple is processed in the fixing sheet. Furthermore, although such a key switch module desirably has a thin thickness so as to be incorporated in the mobile telephone, or the like, the thickness of the key switch increases by the thickness of the resin dimple compared to the conventional thickness since the resin dimple is arranged. Moreover, in the key switch module fabricated in such a manner, a problem in that the resin dimple may drop arises, where the cost further increases if measures are taken to prevent the resin dimple from dropping.
In some key switch modules, a flexible light guide sheet is sandwiched between the fixing sheet and the key, and the light of the light source is introduced into the light guide sheet. In such a key switch module, the light guided through a light guide plate exits from the front surface of the light guide plate by being diffused with a diffusion pattern on the back surface of the light guide plate, where the entire arrayed keys are illuminated from the rear surface side by the light leaked out from the front surface of the light guide plate. However, in the key switch module as disclosed in Patent Document 1, if a light guide sheet made from soft resin is sandwiched between the fixing sheet and the key, the resin dimple is buried in the light guide sheet when the key is pushed, and consequently, the stroke of the key becomes long and the effect of improving the click feeling significantly lowers.
Another key switch module is as disclosed in FIG. 3 of Japanese Unexamined Patent Publication No. 2007-287347 (Patent Document 2). In such a key switch module, the projecting surface side of the contact spring is covered with the fixing sheet and the apex portion of the contact spring is made to adhere to the back surface of the fixing sheet, a projection made from a flexible elastic body is arranged on the front surface of the fixing sheet so as to face the apex portion of the contact spring, and a sheet-like operation member is arranged on the front surface side of the fixing sheet with the projection in between.
The key switch module described in Patent Document 2 satisfies both absorption of manufacturing error in positional relationship between the operation member and the contact spring in a operating direction of the contact spring and thinning in the operating direction of the contact spring by arranging the elastic body between the fixing sheet and the sheet-like operation member, but is not aimed to improve the click feeling.
Even if the elastic body of Patent Document 2 has an effect of improving the click feeling, the elastic body is in the same arrangement as the resin dimple of Patent Document 1 in being arranged at the front surface of the fixing sheet on the side opposite to the contact spring by way of the fixing sheet. Therefore, the key switch module can be thinned compared to when a clearance is formed between the fixing sheet and the operation member as described in Patent Document 2, but the thickness of the key switch module is increased compared to when the elastic body and the clearance are not provided. Furthermore, the cost of the key switch module becomes high since an extra member, that is the elastic body, is required.
In the key switch module of Patent Document 2 as well, the click feeling greatly lowers if the light guide sheet is sandwiched between the fixing sheet and the operation member, similar to Patent Document 1